1. Field of the Invention
The invention relates generally to the controlled administration of medical fluid and, more particularly, to intravenous fluid delivery implementing a control loop to achieve and automatically maintain a desired delivery parameter.
2. Description of the Related Art
Intravenous (“IV”) fluid delivery systems are used to deliver medical fluid to patients at controlled rates. Many such IV fluid delivery systems exist and in one case, precise infusion pumps have been developed to more accurately provide medical fluids to patients in accordance with physician prescriptions. In most cases, an open-loop pump control system is used in which a processor varies the speed of a fluid pump based on a predefined function of various parameters, such as fluid type, infusion profile, and programmed flow rate. Such processor-controlled, open-loop pump systems can be expensive and are usually complex in that they are highly engineered with close tolerance parts to produce the desired accuracy of fluid delivery.
In most cases, such open-loop pumps do not use any feedback to alter the control over the pumping mechanism. Sensors in the pump or associated with the fluid delivery are usually used to detect alarm conditions associated with peripheral events, such as an excessive amount of air in the fluid delivery line, occlusion of the fluid tubing above or below the pump, and depletion of medical fluid in the container. The highly engineered pumping mechanism and processor control accounts for almost the entire accuracy of the pump. However, the rate of fluid delivery is also affected by the precision of disposable components, such as the tubing, used in the fluid path that conveys the medical fluid to a patient. Variations in the internal diameter and material hardness of tubing and pumping components comprising the disposable components cannot be readily compensated in an open-loop control algorithm since such variations may change with the age of the component and since it is impractical to measure such variations directly. As a result, disposable components subject to tight tolerance specifications must be used in such open-loop systems to ensure accuracy of fluid delivery. The tight tolerance specifications increase manufacturing costs which are ultimately borne by the patient.
Certain closed-loop systems have been disclosed in the art over the years and seek to maintain or increase medical fluid delivery accuracy. In a closed-loop system, a parameter or parameters associated with the fluid delivery process are measured to control the fluid delivery system. Prior closed-loop systems have often determined the flow rate of medical fluid to the patient by indirect means, such as by measuring internal pressure forces on the wall of a fluid passageway or by measuring a fluid pressure gradient across a constriction in the fluid passageway. Some prior systems have attempted to measure actual movement of the fluid in the fluid passageway; however, some such systems were invasive in that they involved physical contact with the medicinal fluid and were not implemented. Others required sensors and processing systems that were expensive and also were not implemented.
Fluid delivery manufacturers strive to provide a high level of fluid delivery accuracy while at the same time strive to control costs to patients. A closed-loop pump system and method could provide useful information about the actual delivery of fluid to the patient and if accurate enough, the pump device itself and disposable administration components could be manufactured with looser tolerances thereby reducing costs to the patient. Such accuracy would enable manufacturers to provide different means for delivering medical fluids to patients, including a reliance, at least partially, on gravity as the force to cause the fluid to flow to the patient.
Hence, those skilled in the art have recognized a need for a more advanced medical fluid delivery system and method using a sensor or sensors that measure actual fluid flow to the patient and use such sensed flow information to regulate the fluid delivery. Those skilled in the art have also noted a need for a lower cost fluid delivery apparatus, including a flow regulator and flow conduits, having looser tolerances on parts so that costs are more controlled. Accordingly, it is desirable to provide a lower cost, less complex system for delivery of medical fluids that reduces costs yet provides accuracy in fluid delivery. The present invention satisfies these and other needs.